Yahweh, via Malachi, noted that Judah had not been faithful. There was an abomination in Jerusalem itself. Judah had profaned the sanctuary of Yahweh. Judah had married the daughter of a foreign god. Perhaps this indicates a non-Jewish woman. Thus, Yahweh was going to cut them off from the tents of Jacob. Anyone involved in any kind of false worship of a foreign god would be cut off from being a witness or bringing offerings to Yahweh. They should be excommunicated.